Measuring AC Main Supply Voltage with Arduino (2)

   In article named Measuring AC Voltage with an AC to AC power adapter from OpenEnergyMonitor I found a interesting solution for measure AC voltage.
   Schematic is

   I use EmonLib library like in article:

   On DSO I see on R1 resistor

and at A2 input of Arduino board (on R4 resistor):

   I use an LED display with 8 digit 7-segment drived by MAX7219 (I present on article namend Modul de afisare cu 8 cifre LED din 7 segmente fiecare controlate de MAX7219

   I use some configuration for LedControl library (dosc at The Arduino LedControl library):

   Test schematic is

   I write main_voltage_emonlib_1.ino sketch and upload in Arduino board:

  I made main supply voltage measured with Arduino (2) movie:

Measuring AC Main Supply Voltage with Arduino

   If you need to measuring AC main supply voltage with Arduino must made some calculation.

   I use a simple schematic:

   I can directly measure the DC voltage on R1 resistor. I use internal reference from Arduino Uno board (compatible board with ATmega328 microcontroller) so maximum value for U2 can be

U2 = U1*(R1+R2)/R1 = 1.1*(1+22)/1=25.3V

  AC voltage U1 so DC voltage U2 = U1*1.41-Udiode

  If we put value in equation

U1 = (U2+Udiode)/1.41

because I use trafo U0 = k * U1.

  For tests, I use a trafo imprinted 220V/2x12V 200mA but if I measeure voltage from secondary coil

I found 11V when main voltage is 220V, so k = 220/11=20. I use an 1N4007 diode and Udiode=0.65V.

  I use an LED display with 4 digit 7-segment drived by TM1637 (who I present on base blog in article named Afisaj cu 4 cifre controlate de TM1637 si Arduino and sketches are at https://github.com/tehniq3/TM1637-display):

   Schematic for display put on Arduino Uno is:

   I write main-voltage_0.ino sketch and upload in Arduino board and I made a movie named main supply voltage measured with Arduino